Ring mills are known particularly in the form of bowl roll mills, roller mills or ring-ball mills. In these the grinding elements which are constructed as rolls, rollers or balls roll on an annular grinding plate, and the grinding pressure is produced by spring tension, hydraulic cylinder, centrifugal force or by the dead weight of the grinding elements.
In such mills an air stream is delivered through an air ring arranged stationary on the outer periphery of the grinding plate, and this air stream takes up the fine components of the comminuted material for grinding which is discharged over the edge of the grinding plate and carries these fine particles upwards, whilst the coarse components fall downwards through the air ring against the air stream and are delivered for example by a mechanical elevator back to the mill.
In the previously known grinding method the air speed is set sufficiently high in the nozzle ring that substantially all of the material which is comminuted to the fineness of the finished product and discharged over the edge of the grinding plate is taken up by the air stream and elevated pneumatically to the separator.
A disadvantage with this known method is the high pressure loss associated with the pneumatic conveying of the fines which necessitates the installation of a considerable fan output and involves substantial energy consumption in operation.
The object of the invention, therefore, is to provide an improved and wherein the pressure loss associated with the pneumatic conveying is reduced so that the necessary fan output is reduced and the energy consumption is lower.